Field Of The Invention
The invention relates to a turbine plant, in particular a steam-turbine plant, including at least two turbine sections, each having a turbine rotor extending along a main axis. The turbine rotors are rigidly connected to one another. Each turbine section has an inner casing accommodating guide blades. At least one of the inner casings is displaceable in axial direction. A thermally expanding thrust element is provided for an axial displacement of the inner casing. The invention also relates to a thrust element per se.
German Published, Non-Prosecuted Patent Application DE 35 22 916 A1 describes a turbo set having at least one low-pressure turbine section, which has an outer casing and an inner casing coaxial thereto, and at least one high-pressure and/or intermediate-pressure turbine section disposed coaxially to and upstream of the low-pressure turbine section. Shafts of the turbine sections are rigidly coupled to one another to form a line of shafting. An axial bearing for the line of shafting is mounted upstream of the low-pressure turbine section. The axial bearing defines a reference plane from which the axial shaft expansion and displacement start. The inner casing is attached to an axially movably mounted end of an axially adjacent turbine-section casing or to a turbine-bearing housing through the use of thrust-transmitting coupling rods. The coupling rods are led out in a thermally movable and vacuum-tight manner through a wall of the outer casing, through the use of sealing elements, which also permit a limited transverse movement. A turbine bearing mounted upstream of the low-pressure turbine section defines a second reference plane from which the axial expansion and displacement of the turbine-section casing supported on the turbine bearing and of the turbine-section casing coupled thereto start.
In that way, an axial displacement of the line of shafting and of the turbine-section casings is effected over virtually the same axial expansion and in the same direction, in the course of which only minimum axial clearances occur between moving-blade and guide-blade rings adjacent one another. The thrust transmission through the use of the coupling rods is placed in the region of thrust-transmitting turbine bearings. In addition, a vacuum-tight leadthrough of the coupling rods is structurally combined with a horizontally thermally movable claw mounting of the inner casing of the low-pressure turbine section. Claw arms of the inner casing extend in a direction parallel to the shaft axis and rest with slidable supporting and guide surfaces on the supports of the associated bearing housing. The coupling rods are frictionally coupled to the claw arms in the region of the turbine bearings. In particular, a diaphragm seal for a vacuum-tight leadthrough is attached in a vacuum-tight manner with an outer annular flange to an end surface of the outer casing of the low-pressure turbine section and with an inner annular flange to a turbine-bearing housing part. The configuration of the sealing elements between seating surfaces on the outer-casing end wall and on the bearing housing, that is between parts of only slight relative displacement, causes the larger thermal displacements of the inner casings to be uncoupled from the sealing elements.
German Published, Prosecuted Patent Application DE-AS 1 216 322 describes a steam or gas turbine having a plurality of turbine sections disposed coaxially one behind the other. The shafts thereof are rigidly coupled to one another and of the casings thereof at least one is axially displaceable and is coupled to a fixed turbine-section casing or bearing block. The low-pressure casings of the turbine are each formed of an outer and an inner casing. The inner casing of the low-pressure turbine is coupled to an adjacent turbine-section casing or a bearing block by a linkage which is led through the wall of the outer casing in a steam-tight and thermally movable manner. The linkage may be a single rod which is sealed off in the outer-casing wall by axially and radially flexible bellows. Furthermore, the linkage may be formed of three axially aligned rods connected to one another in an articulated manner, the center rod of which is axially movable with a sliding fit in a bush of the outer-casing wall. Such a linkage is intended to effect an axial displacement of the casings, through the use of which the axial clearance between the rotor and the casings is kept as constant as possible. In order to change the size of the axial clearance, a change in the length of the casing is possible by changing its temperature. That change in the temperature is carried out by an additional thermal load on the linkage through the use of steam or a liquid.
Such a change in the size of the axial clearance, during which hot steam is passed through a pipe, is described in UK Patent GB 1,145,612. An axially expandable pipe is connected at each of its end surfaces to a rod, which in turn is fastened in each case to the inner casing of a low-pressure turbine section. An axial displacement of the inner casings relative to a turbine rotor is composed of the respective expansion of the inner casings, the expansion of the coupling rods and the expansion of the expansion pipes. The thermal expansion of the inner casings that are coupled to one another is defined starting from a fixed point which is disposed at the outer casing of the low-pressure turbine section lying furthest upstream. This starting point of the thermal expansions of the inner casings differs from the starting point of the thermal expansions of the rotor, which is defined in a bearing lying further upstream. The expansion pipes are connected through respective compensators to the corresponding outer casings of the low-pressure turbine sections, so that the absolute expansion of the system of inner casings and coupling rods has to be absorbed by the compensators. In order to ensure a large degree of constancy between the expansion of the turbine rotor and the system of inner casings and coupling rods, steam is to be fed to the expansion pipes in a predetermined manner. The steam must either be extracted from the steam process or be provided separately. A control and monitoring system is also required, through the use of which the steam required in order to compensate for the axial clearance is directed to the expansion pipes, depending on the operating state of the steam turbines.